The project involves studies of the regulation of histidase, urocanase, threonine dehydratase and glutamine synthetase, all from Pseudomonas putida. One phase of the work is a study of the role of glutamine synthetase in the formation of the histidine-degrading enzymes and threonine dehydratase, especially emphasizing the effect of the nitrogen source for growth on the adenylylation-deadenylylation state of glutamine synthetase and its consequences on threonine dehydratase, histidase and urocanase biosynthesis. Also planned is an examination of the regulation of histidase by adenine and guanine nucleotides, with most effort being devoted to effects of the nucleotides on the quaternary structure as revealed by active enzyme centrifugation. Further work will be conducted on the mechanism of the urocanase reaction, especially the question of the involvement of NAD adduct in catalysis, and the possible isolation of a reaction intermediate, the nature of which may be a covalent substrate-NAD adduct. Threonine dehydratase from P. putida appears to exist in two forms which are interconverted by some mechanism related to the covalent modification of glutamine synthetase. The nature of the forms of threonine dehydratase and their interconversion is the focus of this study.